Medium controller

ABSTRACT

When a medium is stored or removed manually, all slots must be checked to find any change in medium information, and as a result, updating medium storage information takes a long time. A medium controller, having a plurality of media and a medium transfer unit to take a medium in and out of storage and move the medium for reading or writing information, comprises slots in which media are store, sensors each mounted in a slot for detecting whether there is a medium in the slot; a sensor manager for holding a log of the status transitions of the sensors in a period when media are likely to be stored or removed manually and deciding the status transitions; and means for reading medium information. Only when it is decided from a decision result of the sensor manager that the medium has been replaced, the media controller causes the means for reading medium information to read medium information in order to update the medium storage information.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a medium controller formedium-exchange type memory units that is used as peripheral equipmentof a computer (for example, an autoloader in a library of magnetic tapeunits or optical disk units).

[0002] The events, such as opening or closing of the entry/exit door,resetting or stopping power supply for the medium controller, arehereafter referred to as medium entry/exit-enable actions. When powersupply is stopped or a reset button is pressed, it becomes possible toopen or close the door of, the medium storage and, after that, a mediummay be taken out or put into storage. This is the reason why thoseevents are treated as the medium entry/exit-enable actions. Uponrecognizing any of such events, the medium controller has medium storageinformation with the contents before this event automatically updated orthe system site operator issues a command to have the informationupdated.

[0003] Conventionally, when medium storage information is to be updatedautomatically or by the operator issuing a command, the prior-art mediumcontroller is unable to obtain medium entry/exit information becausethere is no sensor to recognize a medium in the medium storage area. Asa solution, generally, the medium transfer unit (accessor) is equippedwith a sensor or a bar-code reader to read a bar code on the medium andthe medium transfer unit is made to access all the medium storage places(hereafter referred to as slots) where media are stored, and each timethe sensor or the bar-code reader, provided for (accompanying) theaccessor, recognizes a medium, the medium storage information isupdated. In the prior-art medium transfer unit, each time some medium isreplaced manually, the medium transfer unit accesses all medium storageplaces as mentioned above, taking a long time. Therefore, there is along waiting time before the medium controller can be accessed from thesystem.

[0004] The conventional medium controller cannot grasp the mediumstorage status unless the medium transfer unit (accessor) sequentiallychecks all the slots; therefore, there are the following two problems.

[0005] The first problem is that, in a medium controller with a verylarge number of media in storage, the accessor checks every slot to seewhat medium is stored. This requires a long time for updating mediumstorage information. For this reason, in many cases, medium storageinformation is updated only when the operator desires. Consequently,when a medium is taken out or put into storage especially by manualoperation, if the operator does not update medium storage information,it follows that the medium storage information does not match the actualstorage status.

[0006] The second problem is that, in a medium controller with fewermedia in storage, medium storage information is updated automatically inmany cases when the condition that media are exchanged occurs, with theresult that each time a medium comes in or out, the medium controller iskept waiting while the medium transfer unit is accessing all the slotsand cannot perform other processing.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to greatly reduce timefor updating medium storage information when a medium entry/exit-enableaction occurs during the backup operation of a computer system,particularly in the operation of the, automatic (unmanned) mediumcontroller. This significant time reduction contributes to a substantialsolution of the problem of waiting time before the medium controller canbe accessed. In addition, because it takes a long time to update themedium storage information in the medium controller with a,large numberof media in storage, the medium storage information is not necessarilyupdated each time a medium entry/exit-,enable action occurs but themedium information is updated only when the operator thinks itnecessary. Therefore, it is another object of the present invention tosolve the problem,of the discrepancy between medium storage informationand the actual storage status. This is accomplished by theabove-mentioned significant reduction in time for updating the mediuminformation because this time saving makes it possible to automaticallyupdate the medium storage information when a medium entry/exit-enableaction occurs.

[0008] According to a first aspect of the present invention, there isprovided a medium controller storing a plurality of media, having amedium transfer unit to take a medium in and out of a storage place toread or write information on the medium and to transfer the medium to aplace where reading and writing information is possible, and managinginformation about media in storage. This medium controller comprisesslots for storing media; sensors, each mounted in each of the slots, fordetecting whether or not there is a medium in the slot; a sensor managerfor holding a log of status of the sensors in a period when media arelikely to be taken in or out manually and deciding changes in the statusof the sensors; and a medium information reader for reading mediuminformation, which identifies a medium, from the medium, wherein when itis decided from a decision result by the sensor manager that the mediumhas been replaced, medium information is read by the medium informationreader to thereby update medium storage information, or when it isdecided that the medium has not been replaced, the medium storageinformation is not updated.

[0009] According to a second aspect of the present invention, a mediumcontroller further comprises a door open detector for detecting that thedoor is open at the medium storage place of the medium controller; adoor closed detector for detecting that the door is closed; a firstmemory for storing medium management information showing what media arestored in which slots; and a second memory for storing medium managementinformation showing what media are stored in which slots at the momentwhen the door close detector detects that the above-mentioned entry/exitdoor is closed, wherein the medium storage information is updated bywriting the medium information, which was read in by the mediuminformation reader, in the first and second memories.

[0010] According to a third aspect of the present invention, there isprovided a medium controller, wherein the sensor manager comprises asensor status holder for storing the current sensor status of therespective slots; a log tracer for holding a log of the sensor status ofthe respective slots when it is found from contents of the sensor statusholder that the entry/exit door is opened; and a log, trace determinerfor checking status changes in sensors from contents of the log tracer,wherein supposing that a sensor status that a medium exists isdesignated as ON and a sensor status that a medium does not exist isdesignated as OFF, when a decision result of the sensor status decisionunit is OFF→ON or ON→ON, the medium information is read in by the mediuminformation reader and when a decision result is ON→OFF, the mediuminformation is erased and when a decision result is OFF→ON→OFF or thatthe sensor status remains unchanged, the medium information is not readin by the medium information reader.

[0011] According to a fourth aspect of the present invention, there isprovided another medium controller storing a plurality of media therein,having a medium transfer unit to take a medium in and out of a storageplace to read or write information on the medium and to transfer themedium to a place where reading and writing is possible, and managinginformation about media in storage. This medium controller comprisesslots for storing media; magazines each including a plurality of theslots; sensors, each mounted in each of the magazines, for detectingwhether or not a medium has been removed from or stored in a slot; asensor manager for deciding detection results of sensors in a periodwhen media are likely to be taken out or stored manually; and a mediuminformation reader for reading medium information, which identifies amedium, from the medium, wherein when it is decided from a decisionresult by the sensor manager that the medium has been replaced, mediuminformation is read by the medium information reader to thereby updatethe medium storage information, or when it is decided that the mediumhas not been replaced, the medium storage information is not updated.

[0012] According to a fifth aspect of the present invention, yet anothermedium controller further comprises a door open detector for detectingthat the door is open at the medium storage place of the mediumcontroller; a door closed detector for detecting that the door isclosed; a first memory for storing medium management information showingWhat media are stored in which slots; and a second memory for storingmedium management information after log tracing showing what media arestored in which slots at the moment when the door open detector detectsthat the above-mentioned entry/exit door is open, wherein the mediumstorage information is updated by writing the medium information, whichwas read in by the medium information reader, in the first and secondmemories.

[0013] According to a sixth aspect of the present invention, there isprovided a control method for use in a medium controller storing aplurality of media therein, having a medium transfer unit to take amedium in and out of a storage place to read or write information on themedium and to transfer the medium to a place where reading and writingis possible, and managing information about media in storage. Thismethod comprises the steps of skipping an updating of medium storinginformation when a status of a sensor remains unchanged in a period whenmedia are likely to be removed and stored manually, said sensor beingmounted in each slot where a medium is stored and detecting whether ornot there is a medium in the slot; and updating the medium storinginformation by reading medium information from the medium via mediuminformation reading means when a change is found in the status of thesensor from a sensor status log and it is decided from contents of saidlog that the medium has been replaced.

[0014] According to a seventh aspect of the present invention, there isprovided another control method for use in a medium controller storing aplurality of media therein, having a medium transfer unit to take amedium in and out of a storage place to read and write information onthe medium and to transfer the medium to a place where reading andwriting information is possible, and managing information about media instorage. This method comprises the steps of skipping an updating ofmedium storing information when a sensor does not detect a medium isremoved from or stored in a magazine in a period when media are likelyto be stored into and removed from storage, said sensor being installedin the magazine having a plurality of slots each storing a mediumtherein and detecting the removal or storing of the medium; and updatingmedium storing information by reading medium information from the mediumin all slots in the magazine via medium information reading means whensaid sensor detects tie storing or removal of the medium and it isdecided from detected contents that the medium has been replaced.

[0015] When a medium entry/exit-enable action occurred, the mediumcontroller according to the present invention confirms the spot in themedium storage where the sensor status has changed from that before theentry/exit-enable action. If there has not been any change in the statusof the sensor, the medium storage information is regarded as unchangedafter the entry/exit-enable action took place and the information is notupdated.

[0016] On the other hand, if a change is found in the status of thesensor, the medium controller confirms changes in the sensor status ofthe respective slots, and updates medium storage information of onlythose slots where the sensor status has changed, and uses this updatedinformation as information after a medium went out and came in.

[0017] More specifically, the medium storage information is updatedaccording to the contents of the status changes of sensors. When amedium is in the slot, let the sensor be ON and when there is no mediumin the slot, let the sensor be OFF. For example, suppose that the mediumcontroller may be able to recognize as follows. When the sensor switchesfrom ON to OFF, the medium has been removed from the slot. When thesensor switches from OFF to ON, a medium has been put in the slot. Whenthe sensor switches from ON to OFF to ON, the medium has been replacedand finally put. When the sensor switches from OFF to ON to OFF, amedium has been temporarily put in the slot and finally removed. If themedium controller can manage medium storage information as mentionedabove, when the sensor switches from ON to OFF (the medium has beenremoved from the slot), the medium controller may erase medium storageinformation in the slot. When the sensor switches from OFF to ON to OFF(the medium has been eventually removed), because the medium storageinformation remains unchanged between before and after removal and entryof a medium, the medium controller may not update the medium storageinformation. When the sensor switches from OFF to ON (a medium has beenput in the slot) and when the sensor switches from ON to OFF to ON (themedium has been replaced), the medium controller may check the mediumstorage status for any change with a sensor or a bar-code readerattached to the medium transfer unit, in other words, may read mediuminformation by which to determine a medium that replaced the previous(hereafter referred to as medium information), and may enter mediuminformation after the change in medium storage information. By thisprocedure, medium storage information can be updated accurately with aminimum of action.

[0018] If the medium controller automatically updates medium storageinformation as described above, processing time can be reduced markedly.Also with a medium controller managing a very large number of media instorage, even if medium storage information is updated when a mediumentry/exit-enable action occurs, a waiting time in which the mediumcontroller cannot be accessed from the system can be shortenedsubstantially. For this reason, it is possible to make a setting suchthat updating of medium storage information by managing sensor status isexecuted automatically without relying on the operator.

[0019] Because the provision of sensors for individual slots costs alarge sum of money, it is possible to install sensors at the rate of onesensor for each group of a certain number of slots (e.g., one for eachmagazine). This method of allocation can be implemented as follows. Forexample, in a case where a sensor is installed for each magazines, themedium controller checks the status of the sensor on each magazine, andthen checks the medium storage status at all slots of the magazine,where a sensor status changed, with a sensor or a bar-code readerattached to the medium transfer unit, and subsequently updates mediumstorage information.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The novel features believed characteristic of the invention areset forth in the appended claims. The invention itself, however, as wellas other features and advantages thereof, will be best understood byreference to the detailed description which follows, read in conjunctionwith the accompanying drawings, wherein:

[0021]FIG. 1 is a flowchart of a first embodiment of the presentinvention;

[0022]FIG. 2 is a flowchart of a second embodiment of the presentinvention;

[0023]FIG. 3 is a conceptual diagram showing the structure of the firstembodiment of the present invention;

[0024]FIG. 4 is a conceptual diagram showing the structure of the secondembodiment of the present invention;

[0025]FIG. 5 is a block diagram showing the first embodiment of thepresent invention;

[0026]FIG. 6 is a medium storage information table of the presentinvention; and

[0027]FIG. 7 is a sensor status log table of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The configuration of a first embodiment of the present inventionwill be described with reference to FIG. 5. The medium controlleraccording to the present invention stores many media therein and isprovided with a medium transfer unit to move a medium from the storageplace to a position where the medium can be taken out or put intostorage or data can be read and written on the medium. The mediumcontroller includes a door open detecting means 19 for detecting thatthe entry/exit door is open; a door closed detector 21 for detectingthat the entry/exit door is closed; sensors 2, each mounted in a slot,for deciding whether or not there is a medium in the slot; a mediumstorage information memory 11 for storing medium management informationshowing what medium is stored in each slot; a temporary memory 12 forreceiving and temporarily storing medium management information at themoment when the door open detecting means 19 detects that the entry/exitdoor is open; sensor managing means 14 for monitoring the output of thesensors 2 to find a change in the status of the sensors 2; mediuminformation reading means 13 for reading medium information from themedium to be identified, and a medium information controller 18 whichcauses the medium information reading means 13 to read mediuminformation when it is required from a decision by the sensor managingmeans 14 to update the medium information and which requires thetemporary memory 12 to update the medium storage information based onthe medium information, and also requires the medium storage informationmemory 11 to update its contents stored.

[0029] As an example of medium information, FIG. 6 shows medium storageinformation organized as a media storage information table in which theslot locations are associated with stored, different pieces ofinformation used to determine media (hereafter referred to as mediuminformation). The sensor managing means 14 includes a sensor statusholder 15 for storing the current status (ON when there is a medium; OFFwhen there is no medium) of the sensor 2 of each slot; a log tracer 16for holding a log of the sensor status of each slot after the door opendetector detects that the entry/exit door is opened; and a log tracedeterminer 17 for detecting status that the entry/exit door is closedchanges in the sensors from contents of the log tracer 16.

[0030]FIG. 7 is a table showing the contents of the log tracer 16, thatis, an example of a log of the sensor status. When the entry/exit doorwas opened, the status of the sensors were written in the spaces underthe column title of the Sensor Status Log 1, and subsequently, everytime the status of a sensor changed, the status of the sensors werewritten in the spaces at the corresponding slots of the columns of theSensor Status Log 2, 3 and so on. For example, at the slot 3, the statusof the sensor was initially ON, and switched to OFF and finally ON themoment the door closed detecting means 21 detected that the door wasclosed. This sequence corresponds to a case where initially a medium wasstored, and then the operator opened and closed the door, during whichthe medium was replaced by another medium. Of course, the result is thesame when the same medium was dismounted and put back in the same place.Even if this is the case, it is safer if the medium is regarded asreplaced.

[0031] The log trace determiner 17 checks which of the patterns shownbelow the status transition of each slot belongs by referring to thetable showing the log of sensor status transitions. The statustransitions are: {circle over (1)} OFF→ON (e.g., slot position 2 in FIG.7); {circle over (2)} ON→OFF→ON (e.g., slot position 3); {circle over (3)}ON→OFF (e.g., slot position 1); {circle over (4)} OFF→ON→OFF (e.g.,slot position 4); {circle over (5)} the case where the status transitionof a sensor does not occur. In other words, the sate of a sensorcontinues to be OFF and does not switch to ON (e.g., slot position 6) orthe sensor status continues to be ON and does not switch to OFF (e.g.,slot position 7). For example, the case of slot 5 corresponds to a casewhere a medium was replaced with another medium, which was furtherreplaced with a third medium, but in this case, to know the finalstatus, knowing that the third medium is in the slot 5 is enough and itshould be decided that the transition in this case is the same as thetransition of OFF→ON in the transition {circle over (1)}. In thetransitions {circle over (4)} and {circle over (5)}, there was no mediumeither at the beginning or the end, and there being no difference insubsequent treatment of these cases, these cases may be categorized asthe same pattern of status transition. In the cases {circle over (1)},{circle over (3)}, {circle over (4)} and {circle over (5)}, thetransition pattern can be known from the initial and final sensorstatus. Only in the case {circle over (2)}, the intermediate status ischecked, and if it is found to be OFF, a decision may be made that thisstatus transition {circle over (2)} corresponds to the pattern {circleover (3)}, or if the intermediate status is found to be not OFF, thestatus transition {circle over (2)} corresponds to the pattern {circleover (5)}.

[0032] Description will now be made of the operation of the firstembodiment with reference to FIG. 1. FIG. 1 is a flowchart of theupdating process of medium storage information when sensors are mountedat all and individual slots. The sensors to be mounted are any of thosewhich can decide whether or not there is a medium in the slot (such asan optical sensor, a contact sensor, or a weight sensor). FIG. 3 showssensors 2, which are for example contact sensors attached to the slots.The medium controller provided with the sensors 2, on receiving outputfrom the door open detecting means 19, recognizes that a mediumentry/exit-enable action, then checks medium storage information beforethe medium entry/exit-enable action occurred and writes the mediumstorage information in the temporary memory 12 (Step 1) . The mediumcontroller records status changes in the sensors in the log tracer 16while the door is open. When the door closed detecting means 21 detectsthat the door is closed, the log trace determiner 17 decides fromcontents of the log tracer 16 whether or not there is a change in thestatus of the sensors 2 of the slots (Step 2).

[0033] When it has been confirmed that there is no change in the statusof the sensors, medium storage information after a medium went out and amedium came in is not updated, so that medium storage information beforeexit or entry of medium is maintained as it is (Step 7). If it could beconfirmed that there is some change in the status of a sensor 2 in Step2, decision is made to which patterns shown below the status transitionsof sensors 2 at the respective slots belong (Step 3). When a decision ismade that the sensor status shifted as ON→OFF, the medium is regarded asremoved, and the associated medium information is erased from mediumstorage information (Step 5). If it is decided that the sensor statusshifted as OFF→ON→OFF, the medium is regarded as stored in the slot buteventually taken out, so that medium storage information is not updated(Step 7).

[0034] If it is decided that the sensor status shifted as OFF →ON, themedium is regarded as stored in the slot, or if it is decided that thesensor status shifted as ON→OFF→ON, the medium is regarded as havingbeen replaced. Consequently, the medium transfer unit moves to theposition of the corresponding slot and a sensor (different from the oneinstalled in the slot, but not shown) or a bar-code reader installed onthe medium transfer unit is used to read and recognize new mediuminformation (Step 4). Medium storage information, checked at Step 1 andrecorded in the temporary memory 12, has the change-affected portiononly updated and becomes new medium storage information after the mediumwent out and came in (Step 6). Steps 2 to 6 are sequentially executedfor all slots (sensors 2) , and by writing the contents of the temporarymemory 12 in the medium storage information memory 11, the process iscompleted.

[0035] The important point to note is that with the slots other thanthose whose sensors are judged to have shifted as OFF →ON or ON→OFF→ON,it is not necessary to execute the process at Step 4 of reading mediuminformation from the medium. This reduces the mechanical movement of themedium transfer unit, which results in a notable effect of increasedprocessing speed.

[0036] Description will next be made of a second embodiment of thepresent invention with reference to the configuration of the system inFIG. 5 and the flowchart in FIG. 2. FIG. 2 is a flowchart of theupdating process of medium storage information in a case where a sensoris mounted on each magazine. Referring to FIG. 4, the sensor 5 has aphoto-sensing device installed at the entrance side of the slots of themagazine to detect incoming and outgoing of a medium. More specifically,the sensor 5 comprises a photoemitter 5 a and a photodetector 5 b todetect a medium 3 passing across the optical path of light 6 emittedfrom the photoemitter 5 a. When a medium 3 passed, the sensor managingmeans 14 shown in FIG. 5 recognizes that a medium entry/exit action tookplace. In the case of the second embodiment, there are two kinds ofstatus changes for one sensor: whether a medium entry/exit-enable actionoccurred or not. Therefore, the log tracer 16 in the sensor managingmeans 14 in FIG. 5 may be omitted.

[0037] When the medium information controller 18 recognizes that amedium entry/withdraw-enable action occurred, it checks medium storageinformation before the medium entry/withdraw-enable action (Step 1).Subsequently, a check is made to see if the status of the sensor 5 ofthe slot has changed (Step 2). If it is confirmed that there is nochange in the status of the sensor, medium storage information beforethe medium input/output enable action is not updated as in FIG. 1 (Step8). For the magazine 7 in which a medium blocked the light of theoptical sensor 5 attached to the magazine 7, the status of medium changeis checked for all slots of the magazine by the medium informationreading means 13 through a sensor mounted on the medium transfer unit(not shown) or a bar-code reader (not shown) (Steps 4 and 5).

[0038] The whole medium storage information in the magazine may beupdated. Alternatively, however, a decision is made for each slot asshown in FIG. 2, and if the decision is that a medium does not exist(Step 4) , medium information is erased (Step 7). On the other hand, ifthe decision is that there is a medium in the slot (Step 4), a decisionis made whether or not medium information of the slot has changed, andif the decision is that the medium information remains the same, it isconcluded that the medium information need not be rewritten as far asthis slot is concerned and this Step is carried out for the next slot(Steps 9 and 10), and if the decision is that the medium information haschanged, the medium information that has been read is written in thetemporary memory 12 so that medium storage information is updated (Step6). After this, if all slots in the magazine have not been checked (Step9), medium information of the next slot is read (Step 10) , and adecision is made whether or not a slot is stored in the next slot (Step4). Subsequently, this procedure is repeated until all slots have beenchecked. When all slots in the magazine have been checked (Step 9), theprocess for this magazine is finished. When the process for one magazineis finished and if there is another magazine where there were outgoingand incoming of a medium, the same process is executed on this magazine.

[0039] Besides the above-mentioned optical sensor, another method bywhich to make the medium controller to decide whether a medium went inand out is by a weight sensor, which detects a change in the weight ofthe magazine.

[0040] If medium information is updated every time a medium goes out ofor into the magazine, accurate and quick updating of medium storageinformation can be achieved. More specifically, when a mediuminput/output-enable action occurred, inquiry is made only of the placewhere a change occurred (into all slots of the change-involved magazine)without checking all medium storage places (slots) with a sensor or abar-code reader mounted on the medium transfer unit. In other words, itis not necessary to check the slots of the magazine where no changeoccurred, with a sensor or through bar codes and accordingly, processingspeed becomes faster than in prior art.

[0041] Supplementary explanation of the preferred embodiments andapplications of the present invention will be given in the following.

[0042] Description will be made of how the sensors 2 are mounted. FIG. 3shows an example wherein switch sensors 2 are mounted in all slots andFIG. 4 shows an example wherein an optical sensor 5, consisting of asensor photoemitter 5 a and a sensor photodetector 5 b, is mounted atthe medium entrance of the magazine, both of which can be realizedeasily. Mounting sensors in individual slots costs a large amount ofmoney, but if an optical sensor is mounted for each magazine as shown inFIG. 4, this arrangement is less expensive. In FIG. 3, the conditionthat a sensor is pressed by a medium placed in the medium storage placeis designated as ON and the condition that a sensor is not pressed by amedium because there is no medium in the storage place is designated asOFF. In FIG. 4, when light 6 emitted by the photoemitter 5 a is blockedin a given magazine, the medium controller can recognize that a mediumwent in or out of some slot in the magazine.

[0043] Next, description will be made of cases where the presentinvention can be applied. There is a risk that the medium controller isunable to obtain medium storage information because of some humanintervention, for example, in the input or output of a medium to or frommedium storage for medium managing or in the maintenance work of themedium controller. When there is human intervention, any of the actionsoccurs, such as opening and closing of the entry/exit door, stopping orsupplying power to the medium controller. The medium controller candetect the occurrence of those events easily by well-known technology.

[0044] When there is human intervention in the operation of the mediumcontroller, in other words, when the medium entry/exit door is openedand then closed, or the power to the medium controller is turned offthen on, or system reset, the medium controller recognizes that any ofthose events took place, by using well-known technology. By replacingthe door open detecting means 19 in FIG. 5 by human interventiondetecting means, a reset system action and medium controller poweroff-on action being taken can be considered to be the same as theentry/exit door being opened or closed. Then, when the entry/exit doorwas opened or closed and a reset system action and a medium controllerpower off-on-action was taken, the medium controller calls a mediumstorage information table from the medium storage information memory 11into the temporary memory 12. Subsequently, the log trace determiner ofthe sensor managing means 14 finds a change in the sensor 2 to recognizethat a medium was taken in or out, and updates only the change-relatedportion of medium storage information in the temporary memory 12. Afterhuman intervention, whenever a job is executed by the host computer andconsequently medium storage information is updated, medium storageinformation in the temporary memory 12 is updated. After the job isterminated, medium storage information of the latest version is storedin the medium storage information memory 11.

[0045] When the power was switched off and if power supply for theprocess shown in FIG. 1 is provided as a separate system and can beused, the same operation as mentioned above can be performed. Even ifpower supply is not provided as a separate system, it is possible tograsp just like the medium status when the power is switched off and on.Namely, door open operation is replaced with power off operation anddoor close operation is replaced with power on operation and in FIG. 5and a door close detector 21 is replaced with power on detector, afterpower is switched on, medium information before power off operation isput in the sensor status holder and medium information after power onoperation is put in the log holder. Then medium information is updatedin log tracer determiner, and it is easy to determine status changes.

[0046] In updating medium information proposed by the present invention,accurate and high-speed updating of medium storage information can beachieved by checking only the place where a change occurred (a slot inthe first embodiment in FIG. 3 or a magazine in the second embodiment inFIG. 4) without having to check all slots with a sensor or a bar-codereader attached to the medium transfer unit when a mediumstorage/exit-enable action took place.

[0047] In the process for updating medium storage information accordingto the present invention, as has been described, a medium controller isused, which includes means for recognizing, for example, that theentry/exit door is opened or closed and that power supply for the mediumcontroller is disconnected or supplied, and simple sensors arranged atindividual slots and each capable of recognizing whether or not a mediumis stored in the slot or sensors arranged at individual magazines andeach capable of recognizing whether or not a medium is put in or takenout of the slot. Therefore, when a medium entry/exit-enable action tookplace, the process for updating medium storage information need notcheck all slots with a sensor or a bar-code reader arranged on themedium transfer unit, but has only to check the place where a changeoccurred (a slot or a magazine) to update medium storage information.This configuration allows medium storage information to be updatedeasily, accurately, and speedily.

[0048] Therefore, time required for updating medium storage informationcan be shortened sharply, with the result that the present inventionoffers an effect to solve the problem that the medium controller is madeto wait and cannot execute other processes while the medium transferunit accesses all the slots each time a medium comes in or goes out. Ina medium controller with a large number of media in storage, in whichtime-consuming medium-storage-information updating job is done by anoperator, the present invention makes it possible to automaticallyupdate medium storage information without intervention by the operatorafter a medium entry/exit-enable action took place, and thus precludesthe problem that medium storage information does not agree with theactual storage status.

[0049] While this invention has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to persons skilled in the art upon reference to thisdescription. It is, therefore, contemplated that the appended claimswill cover any such modifications or embodiments as fall within the truescope of the invention.

What is claimed is:
 1. A medium controller storing a plurality of mediatherein, having a medium transfer unit to take a medium in and out of astorage place to read or write information on the medium and to transferthe medium to a place where reading and writing information is possible,and managing information about media in storage, comprising: slots forstoring media; sensors, each mounted in each of the slots, for detectingwhether or not there is a medium in said slot; a sensor manager forholding a log of status of said sensors in a period when media arelikely to be taken in or out manually and deciding changes in the statusof said sensors; and a medium information reader for reading mediuminformation, which identifies a medium, from the medium, wherein when itis decided from a decision result by said sensor manager that the mediumhas been replaced, medium information is read by said medium informationreader to thereby update medium storage information, or when it isdecided that the medium has not been replaced, said medium storageinformation is not updated.
 2. A medium controller according to claim 1,further comprising: a door open detector for detecting that the door isopen at the medium storage place of the medium controller; a door closeddetector for detecting that the door is closed; a first memory forstoring medium management information showing what media are stored inwhich slots; and a second memory for storing medium managementinformation showing what media are stored in which slots at the momentwhen said door close detector detects that said entry/exit door isclosed, wherein said medium storage information is updated by writingsaid medium-information, read in by said medium information reader, inthe first and second memories.
 3. A medium controller according to claim2, wherein said sensor manager comprises a sensor status holder forstoring current sensor status of the respective slots; a log tracer forholding a log of the sensor status of the respective slots when it isfound from contents of the sensor status holder that said entry/exitdoor is closed; and a log trace determiner for checking status changesin sensors from contents of said log tracer, and wherein supposing thata sensor status that a medium exists is designated as ON and a sensorstatus that a medium does not exist is designated as OFF, when adecision result of the sensor status decision unit is OFF→ON or ON→ON,said medium information is read in by said medium information reader andwhen a decision result is ON→OFF, said medium information is erased andwhen a decision result is OFF→ON→OFF or that the sensor status remainsunchanged, said medium information is not read in by said mediuminformation reader.
 4. A medium controller storing a plurality of mediatherein, having a medium transfer unit to take a medium in and out or astorage place to read or write information on the medium and to transferthe medium to a place where reading and writing is possible, andmanaging information about media in storage, comprising: slots forstoring media; magazines each including a plurality of said slots;sensors, each mounted in each of the magazines, for detecting whether ornot a medium has been removed from and stored in a slot; a sensormanager for deciding detection results of sensors in a period when mediaare likely to be taken out or stored manually; and a medium informationreader for reading medium information, which identifies a medium, fromthe medium, wherein when it is decided from a decision result by saidsensor manager that the medium has been replaced, medium information isread by said medium information reader to thereby update said mediumstorage information, or when it is decided that the medium has not beenreplaced, said medium storage information is not updated.
 5. A mediumcontroller according to claim 4, further comprising: a door opendetector for detecting that the door is open at the medium storage placeof said medium controller; a door closed detector for detecting that thedoor is closed; a first memory for storing medium management informationshowing what media are stored in which slots; and a second memory forstoring medium management information showing what media are stored inwhich slots at the moment when the door close detector detects that saidentry/exit door is open, wherein said medium storage information isupdated by writing said medium information, read in by said mediuminformation reader, in the first and second memories.
 6. A mediumcontroller storing a plurality of media therein, having a mediumtransfer unit to take a medium in and out of a storage place to read orwrite information on the medium and to transfer the medium to a placewhere reading and writing information is possible, and managinginformation about media in storage, comprising: slots for storing media;sensors, each mounted in each of the slots, for detecting whether or notthere is a medium in said slot; means for deciding changes in status ofthe sensors in a period when media are likely to be taken in or outmanually; and means for reading medium information, which identifies amedium, from the medium, wherein when it is decided from a decisionresult by said means for deciding changes in the status of the sensorsthat the medium has been replaced, medium information is read by meansfor reading medium information to thereby update medium storageinformation, or when it is decided that the medium has not beenreplaced, said medium storage information is not updated.
 7. A mediumcontroller according to claim 6, further comprising: means for detectingthat the door is open at the medium storage place of said mediumcontroller; means for detecting that said door is closed; first memorymeans for storing medium management information showing what media arestored in which slots; and second memory means for storing mediummanagement information showing what media are stored in which slots atthe moment when said door close detecting means detects that saidentry/exit door is closed, wherein said medium storage information isupdated by writing said medium information, read into by said mediuminformation reading means, into said first and second memory means.